In today's energy conscious environment, great effort is being made to increase the energy efficiency of heat transfer devices. In order to meet future increased efficiency demands for refrigerators, it is important to look at every aspect of the packaged unit that has an impact on the overall efficiency. Generally, efficiency increases can cost more money per unit, take up more space and/or be limited by physical or thermodynamic limitations.
In general, fins are used to increase the heat transfer capacity or to maintain a heat transfer capacity while reducing the other requirements, such as space, temperature differential, and conductive heat transfer media. There are many design tradeoffs that go into determining an optimal solution. Examples of such tradeoffs are type of material used, the space available, air flow rate, and the expense of material used.
The controlling formula for fin design, as far as thermal performance is concerned, is: ##EQU1## Where
h.sub.c =Convective Heat Transfer Coefficient PA1 L.sub.c =L+t/2 PA1 L=Length of Fin PA1 t=Thickness PA1 K=Thermal Conductivity of Fin Material
The size and orientation of the fin with respect to the tube is also a factor to consider due to the limited amount of space in a typical forced draft condenser.
Another major difficulty is the attaching of two dissimilar metals. The attachment of two dissimilar metals can result in a corroding action from a bi-metal galvanic potential. The reaction and rate of corrosion depends on the two types of metal used and the conductive media they are immersed in.
A number of prior art references are directed towards increasing the efficiency of serpentine coil heat transfer devices. Systems designed to achieve these results are disclosed, for example, in U.S. Pat. Nos. 1,786,571 (Longsdale); 3,279,535 (Huet); 4,285,397 (Ostbo); and 4,580,623 (Smitte et al.).
The Longsdale patent discloses the use of a lateral fin on a tube for improving heat exchange. The fin is an integral part of the tube and thus avoids welding the fin to the tube.
The Huet patent discloses the use of a tube with a lateral fin attached to the exterior surface of the tube. The tube is bent in a serpentine arrangement for improved heat transfer. At each bend, triangular shaped cuttings are removed from the fins.
The Ostbo patent discloses the use of a tube with lateral fins. The tubes are positioned so as to allow the fins to form a plate-like structure between the tubes.
The Smitte et. al. patent discloses the use of tubes with lateral fins in a serpentine arrangement. Sets of tubes are staggered so as to increase the number of tubes. The fins are positioned so as to allow contact between the two tubes.
Other prior art references which disclose tubes with lateral fins in various configurations include U.S. Pat. Nos. 2,434,519 (Raskin); 2,646,972 (Schmid); 4,399,660 (Vogler et al.); and 4,966,230 (Houghes et al.).
Although all of the above-discussed devices relate to serpentine coil heat transfer devices with lateral fins, the prior art structures do not effectively solve the space and cost problems associated with refrigeration devices.